Lowering preamp voltages

[iknowjohnny]

I know this is a stupid question, but then when it comes to electronic theory i'm pretty dang stupid so WTH.....Is it typical practice to lower preamp voltages by raising plate resistors rather than using larger dropping resistors at the PSU node? I always thought you would use the PSU resistors to do that, but i notice amps typically seem to use the same dropper value for every node which tells me if they want different voltages at various preamp stages, it might be the different value plate R's at different stages they use in a lot of amps that are there for that purpose. I was always led to believe you use a given plate R value depending on the gain you want. Thoughts?

[martin manning]

Is it typical practice to lower preamp voltages by raising plate resistors rather than using larger dropping resistors at the PSU node?

No.

I always thought you would use the PSU resistors to do that,

Yes.

but i notice amps typically seem to use the same dropper value for every node which tells me if they want different voltages at various preamp stages, it might be the different value plate R's at different stages they use in a lot of amps that are there for that purpose.

No.

I was always led to believe you use a given plate R value depending on the gain you want.

Yes.

The operating point is determined by the combination of supply voltage, plate load, and cathode resistor, so they are not completely unrelated.

[matt h]

(deleted)

[iknowjohnny]

Ok, if thats the case tho, then i guess few or no amp's are designed with the idea that they might want a different voltage for different stages? I ask because i generally never see dropping R's of different values at various preamp nodes. yet it seems like that could be a good way to get what you want when designing an amp with cascaded pre stages.

[vibratoking]

Here is a great explanation of triode gain stages if you haven't seen it already:
http://www.valvewizard.co.uk/Common_Gain_Stage.pdf

[brewdude]

I think the reason you don't see much variation in resistor values is that the low current draw of the triodes in the preamp, likely makes decoupling resistors less effective at dropping voltage.

[Jana]

It's cheaper to buy and stock 10,000 10K resistors than it is to buy and stock 2000 10K, 2000 6.8K, 2000 8.2K, 2000 4.7K, and 2000 12K.

[Teleguy61]

It's cheaper to buy and stock 10,000 10K resistors than it is to buy and stock 2000 10K, 2000 6.8K, 2000 8.2K, 2000 4.7K, and 2000 12K.

Reality.